Does it only happen on one side?
Check things like:
Is the crank arm tight?
Is the pedal tight? (It's also a good idea to grease the pedal threads before installing)
Are the bearings in both the bottom bracket and pedals lubed and well-adjusted?

Check what position the crank arm is in when it knocks, is it the same place every single time you get it, also try pedaling lightly without putting load on the pedals and see if it still does it.

I had a similar knocking on my bike when I first bought it new, it would make a knocking noise when the non drive crank arm was going from straight up to forward with my pedaling load on it.

I took the crank arm off to make sure the inside was still square with no burrs and it was fine, I put it back together nice and tight with some loctite on the crank bolt, since then it's been quiet as a mouse.

I guess it hadn't been put together properly when made or assembled in the bike shop.

With all due respect, I'm not sure I would recommend locktite on the crank bolt. I know that there are different "strengths" of the product, but I've never seen a need for using it on a crank bolt. If the spindle tapers are in good condition, along with the flats in the crank arm hole, all you really should need is a coat of grease on the bolt threads. Don't apply grease to the spindle flats or in the crank arm hole. I've practiced this procedure for over 25 years, being tested with everything from sprints to mountain climbs, and have never had a crank loosen up.

Not good. Put grease there. otherwise aluminum will fuse to the steel and make removal at least difficult. One bike shop here did exactly that (I believe) when I still had no clue. I stripped the threads of the crank arm and had to resort to destructive force when I wanted to swap the bottom bracket for a new one.

There are two camps about greasing crank arms.
One thought is, if greased, this allows the arm to slide too easily on the crank which may give rise to spreading of the square hole when being tightened.
The other if not greased will cause the crank arm to jam up as Joe explains.
Me, I make sure that the hole and crank spindle is clean but with just the very slightest smear of grease. Especially if not expecting to remove them for an extended period of time.
I would not though use any form of thread lock on it. In fact I never use thread lock on any parts of my bikes. Usually I check the tightness after a few rides on a new installation.

(03-15-2010, 07:34 PM)cyclerUK Wrote: Me, I make sure that the hole and crank spindle is clean but with just the very slightest smear of grease.

Yes, I would suggest the thinnest film.

Joe: I'm not saying that there has never been a crank arm seize onto the spindle. But in all my years, I have never seen one. I should clarify my original statement about not putting any grease on the spindle:

When I overhaul a BB, my fingers have a small film of grease on them from applying it to the BB cups, even after wiping them on a rag. Whatever is left on my fingers (not enough to actually see), that is what ends up getting wiped on the spindle flats.

Ok marke, in that case I fully agree with you. It happened to me last year, so the pain is still fresh though the bad shop might have overtightened it, too (and badly). Oh, and the guy at my favorite LBS also said he had never seen this before, and he has been in business for several decades. Another reason to a) stay with the shop you know (he had holiday at that time, so I couldn't) or b) do your own maintenance (old Stronglight crankset -> don't have the tool -> couldn't do that).

I used the lightest type of locktite on pedals recently, stupid cheapo dual purpose (one side flat, other side SPD) pedals, SPD mechanism always comes loose.

Maybe Copper grease instead as a middle ground? It's not really a lubricant; its main purpose is as an anti-seize compound, particularly in areas with bad weather.

I don't know where you live Marke, but here in Wales we go MTBing in pretty bad weather quite often (even during the winter). It's quite common for loads of things to seize out there and you really do have to look after your bike; and yes I have seen a few seized crank bolts.